Engine, Gearbox & Propeller Calculators
Estimate engine power for displacement boats, calculate propeller diameter and gearbox ratio, or verify whether an existing engine, gearbox and propeller setup looks balanced. These tools are planning estimates and are simplified planning estimates.
Units
Vessel details
Full load displacement including fuel, water, stores and crew.
kg
The cruising speed you want to achieve at full load.
knots
Length of the hull at the waterline, used to calculate theoretical hull speed.
m
For displacement boats.
This engine power calculation is intended for displacement hulls. It is not suitable for planing boats.
Engine power requirement
Recommended engine power
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Calculated minimum
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Equivalent HP
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Reserve added to estimate
25%
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Calculation method – engine power
This calculation is for displacement boats only.
Power (HP) = (Displacement in tonnes ^ 2/3 × Speed³) / 45
The calculated minimum is converted to kW, and the recommended estimate includes a fixed planning reserve of 25%:
Recommended estimate = calculated minimum × 1.25
Hull speed reference:
Hull speed (knots) = 1.34 × √waterline length in feet
This is an estimate. This is our best estimate based on the entered values and a simplified planning model. Propeller pitch, hull condition, loading and real operating conditions can affect the final setup.